Electric field emission device having a triode structure fabricated by using an anodic oxidation process and method for fabricating same

ABSTRACT

An electric field emission device having a triode structure is fabricated by using an anodic oxidation process. The device includes a supporting substrate, a bottom electrode layer to be used as an cathode electrode of the device, a gate insulating layer having a plurality of first sub-micro holes, a gate electrode layer having a plurality of second sub-micro holes connecting to the first sub-micro holes, an anode insulating layer having a plurality of third sub-micro holes connecting to the second sub-micro holes, a top electrode layer for hermetically sealing the device, the top electrode layer being used as an anode of the device and a plurality of emitters formed in the first sub-micro holes. The emitters are formed so as to come into as close contact as possible to the electrodes of the device, which results in decreasing a driving voltage.

TECHNICAL FIELD

The present invention relates to an electric field emission device and amethod for fabricating same; and, more particularly, to an electricfield emission device having a triode structure fabricated by using ananodic oxidation process and a method for fabricating same.

BACKGROUND ART

In general, an electric field emission device means a device whereelectrons are emitted from a surface of metal or semiconductor in avacuum in accordance with tunneling effect caused by applying electronicfield having high intensity to the surface. Such an electric fieldemission device may be utilized as a high-speed switching device, amicrowave generator, an amplifier or a display device. In the device,the emitted electrons can induce high power at a high frequency in avacuum with low energy loss. Further, the device has several advantagesthat it has a shorter response time than a conventional solid-statedevice and may be integrated on a single silicon chip.

FIG. 1 illustrates a cross-sectional view of a conventional “Spindt”type electric field emission device having a triode structure fabricatedby using an electron beam photolithographic process.

Referring to FIG. 1, the electric field emission device is fabricated asfollows. That is, on a glass or a silicon substrate 100, a cathode layer102, a resistive layer 104, an insulating layer 106 and a gate electrodelayer 108 are formed sequentially. And then, photosensitive filmpatterns, each having a diameter of micrometer, are formed on the gateelectrode 108 by using a photolithographic process. Thereafter, theinsulating layer 106 is etched by using a reactive ion etching techniquesuch that a surface of the resistive layer 104 is exposed. Subsequently,a metal electric field emission tip 110 containing material such as Mo,W and Cr is vertically deposited on the resistive layer 104 to have aconical shape by using an electron beam evaporation technique.

As mentioned above, the Spindt type electric field emission device hasadvantages that it has a shorter response time than a conventionalsolid-state device and may be integrated on a single silicon chip.However, it is difficult to arrange a plurality of micro holes atregular intervals on the electric field emission device as shown in FIG.1, particularly when an area of the surface of the device is large.Further, since a distance between an electric field emission tip and ananode electrode is several hundreds micrometers, the electric fieldemission device as shown in FIG. 1 has a disadvantage that it requires ahigh driving voltage. Furthermore, there may be needed an additionalprocess to form micro holes, each having a sub-micrometer diameter, onthe surface of the gate electrode layer 108.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to provide anelectric field emission device having a triode structure wherein anarray of gate holes, each having a sub-micrometer diameter, are formedthereon by using an anodic oxidation process, to thereby facilitate anarrangement of the gate holes at regular intervals even on a large area,and emitter tips are formed to get a close contact to electrodes, tothereby decrease a driving voltage for the device.

In accordance with one aspect of the present invention, there isprovided an electric field emission device having a triode structurefabricated by using an anodic oxidation process, comprising: asupporting substrate; a bottom electrode layer formed on the supportingsubstrate, which is used as an cathode electrode of the device; a gateinsulating layer formed on the bottom electrode layer, having aplurality of first sub-micro holes to be used as gate holes of thedevice; a gate electrode layer formed on the gate insulating layer,having a plurality of second sub-micro holes each connecting to acorresponding one of the first sub-micro holes; an alumina layer formedon the gate electrode layer, having a plurality of third sub-micro holeseach connecting to a corresponding one of the second sub-micro holes; atop electrode layer for hermetically sealing the device in a vacuum,which is formed on the alumina layer and used as an anode of the device;and a plurality of emitters for emitting electrons in a high electricfield, each of the emitters being formed in a corresponding one of thefirst sub-micro holes.

In accordance with another aspect of the present invention, there isprovided an electric field emission device having a triode structurefabricated by using an anodic oxidation process, comprising: asupporting substrate; a bottom electrode layer formed on the supportingsubstrate, which is used as an cathode electrode of the device; a gateinsulating layer formed on the bottom electrode layer, having aplurality of first sub-micro holes to be used as gate holes of thedevice; a gate electrode layer formed on the gate insulating layer, thegate electrode layer having a plurality of second sub-micro holes eachconnecting to a corresponding one of the first sub-micro holes; an anodeinsulating layer formed on the gate electrode layer, having a pluralityof third sub-micro holes each connecting to a corresponding one of thesecond sub-micro holes; a top electrode layer for hermetically sealingthe device in a vacuum, which is formed on the anode insulating layerand used as an anode of the device; and a plurality of emitters foremitting electrons in a high electric field, each of the emitters beingformed in a corresponding one of the first sub-micro holes.

In accordance with still another aspect of the present invention, thereis provided a method for fabricating an electric field emission devicehaving a triode structure by using an anodic oxidation process,comprising the steps of: (a) forming a bottom electrode layer on asupporting substrate, the bottom electrode layer being used as ancathode electrode of the device; (b) forming sequentially a gateinsulating layer, a gate electrode layer and an aluminum layer on thebottom electrode layer; (c) forming a plurality of first sub-micro holesin an alumina layer by performing an anodic oxidation process on thealuminum layer, thereby transforming the aluminum layer into the aluminalayer; (d) etching a barrier layer of the alumina layer and the gateelectrode layer, thereby a surface of the gate insulating layer beingexposed through the first sub-micro holes; (e) forming a plurality ofsecond sub-micro holes in the gate insulating layer, thereby each of thefirst sub-micro holes connecting to a corresponding one of the secondsub-micro holes; (f) forming an emitter for emitting electron in a highelectric field in each of the second sub-micro holes; and (g) forming atop electrode layer for hermetically sealing the device on the aluminalayer in a vacuum, the top electrode layer being used as an anode of thedevice.

In accordance with still another aspect of the present invention, thereis provided a method for fabricating an electric field emission devicehaving a triode structure by using an anodic oxidation process,comprising the steps of: (a) forming a bottom electrode layer on asupporting substrate, the bottom electrode layer being used as ancathode electrode of the device; (b) forming sequentially a gateinsulating layer, a gate electrode layer, an anode insulating layer andan aluminum layer on the bottom electrode layer; (c) forming a pluralityof first sub-micro holes in an alumina layer by performing an anodicoxidation process on the aluminum layer, thereby transforming thealuminum layer into the alumina layer; (d) etching an barrier layer ofthe alumina layer, the anode insulating layer and the gate electrodelayer, thereby a surface of the gate insulating layer being exposedthrough the first sub-micro holes; (e) forming a plurality of secondsub-micro holes in the gate insulating layer, thereby each of the firstsub-micro holes connecting to a corresponding one of the secondsub-micro holes; (f) removing the alumina layer; (g) forming an emitterfor emitting electron in a high electric field in each of the secondsub-micro holes; and (h) forming a top electrode layer for hermeticallysealing the device on the anode insulating layer in a vacuum, the topelectrode layer being used as an anode of the device.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description of preferred embodiments,given in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a cross-sectional view of a conventional electricfield emission device having a triode structure fabricated by using anelectron beam photolithographic process;

FIGS. 2A to 2F describe cross-sectional views of an electric fieldemission device having a triode structure fabricated by using an anodicoxidation process in accordance with a first preferred embodiment of thepresent invention; and

FIGS. 3A to 3F exhibit cross-sectional views of an electric fieldemission device having a triode structure fabricated by using an anodicoxidation process in accordance with a second preferred embodiment ofthe present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 2A to 2F present cross-sectional views of devices, each of whichis fabricated in each step of a method for fabricating an electric fieldemission device having a triode structure by using an anodic oxidationprocess in accordance with a first preferred embodiment of the presentinvention. In the following, the method in accordance with the firstpreferred embodiment of the present invention will be described indetail.

First, as shown in FIG. 2A, the bottom electrode layer 202 containing,e.g., W, Cr, Nb, Al, Ti or alloy thereof is formed on the supportingsubstrate 200 containing non-conducting material such as glass, e.g., byusing a sputtering method or an electron beam deposition method. Insteadof the above-mentioned metal, the bottom electrode layer 202 may containconductive polymer substance, metallic oxide, metallic nitride ormetallic sulfide. The thickness of the bottom electrode layer 202 ispreferably about 2000 Å.

Thereafter, the resistive layer 204 and the gate insulating layer 206are sequentially formed on the bottom electrode layer 202 by using theLPCVD method or a reactive sputtering method. Herein, the resistivelayer 204 and the gate insulating layer 206 may contain SiO₂ or metallicoxide. Further, the thickness of the resistive layer 204 preferablyranges about from 10 Å to several tens Å.

In the meantime, although the resistive layer 204 has been described tobe formed between the gate insulating layer 206 and the bottom electrodelayer 202, the formation of the resistive layer 204 may be omitted.

Then, on the gate insulating layer 206, the gate electrode layer 208containing one of Au, W, Nb, Cr, Al and Ti and the aluminum layer 210are sequentially formed by using a sputtering method. Instead of theabove-mentioned metal, the gate electrode layer 208 may containconductive polymer material, metallic oxide, metallic nitride andmetallic sulfide. The thickness of each of the gate insulating layer 206and the aluminum layer 210 is preferably about 500 nm.

Next, as shown in FIG. 2B, the aluminum layer 210 is processed by usingan anodic oxidation process to become an alumina layer 212 havingsub-micro holes 213 therein. The anodic oxidation process is performedas follows. That is, a surface of the aluminum layer 210 is polished byusing an electropolishing method. The aluminum layer 210 is then dippedin a solution of phosphoric acid, oxalic acid, chromic acid or sulfuricacid and a DC voltage ranging about from 10 V to 200 V is appliedthereto, thereby forming the alumina layer 212 having the sub-microholes 213 therein. In particular, it is preferable to apply a DC voltageof 25 V, 40 V or 195 V to the aluminum layer 210 in order to form thesub-micro holes in the form of a honeycomb.

Subsequently, as shown in FIG. 2C, the barrier layer 214 of the aluminalayer 212 and the gate electrode layer 208 is dry-etched by using areactive ion etching method in an atmosphere of a gas mixture of CF₄ andO₂, such that a surface of the gate insulating layer 206 is exposed.Alternatively, the barrier layer 214 of alumina layer 212 and the gateelectrode layer 208 may be etched by using ion milling or wet etchingtechniques.

Then, as illustrated in FIG. 2D, the gate insulating layer 206 is etchedto have sub-micro holes therein connecting to the corresponding holes ofthe alumina layer 912. In etching the gate insulating layer 206, theremay be employed one of ion milling, dry etching, wet etching and anodicoxidation techniques. Each of thus formed sub-micro holes preferably hasa depth ranging about from 500 nm to 1 μm.

Thereafter, as shown in FIG. 2E, emitters 218 are formed in the holes ofthe gate insulating layer 206. The emitters 218 may be formed by growingmetal from bottoms of the holes or by attaching metal to bottoms of theholes. In this case, the emitters 218 is preferably formed to come intoas close contact as possible to the gate electrode layer 208, whichresults in decreasing a driving voltage for the electric field emissiondevice of the present invention.

The growth of the metal in the holes is performed by applying DC or ACvoltage (or current) or voltage (or current) pulse to the structure(e.g., the bottom electrode layer 202) shown in FIG. 2D in a solution ofmetal sulfate, metal nitrate or metal chloride. The height of thegrowing metal depends on a time period of applying the voltage. Further,the process of growing the metal may be carried out after chemicallyactivating surfaces of the bottoms of the holes. Herein, the metal usedin forming the emitters 218 may contain, e.g., Au, Pt, Ni, Mo, W, Ta,Cr, Ti, Co, Cs, Ba, Hf, Nb, Fe, Rb or alloy thereof.

On the other hand, the emitters 218 may be formed by using a carbonnano-structure such as a carbon nano-tube, a carbon nano-fiber, a carbonnano-particle and an amorphous carbon material. Particularly, it ispreferable that the carbon nano-tube is used as the emitters 218 sinceit has such desirable characteristics as high mechanical solidity, highchemical stability and high field enhancement factor.

In the first embodiment of the present invention, the carbon nano-tubesto be used as the emitters 218 may be formed by decomposing thermally orin plazma a gas mixture of hydrocarbon, carbon monoxide, hydrogen and soon at about 200-800°C.

Alternatively, the emitters 218 may be grown in the holes, e.g., bythiolizing a pre-synthesized carbon nano-tube and applying thereto anAu-S chemical composition process. That is, the pre-systhesized carbonnano-tube is dipped into an acid solution and then into a solutioncontaining a group including sulfur, such that a functional groupcontaining sulfur (S) is attached to the carbon nano-tube. Then, thesulfur (S) attached to the carbon nano-tube is coupled to gold formed ona surface of the bottoms of the holes.

The process of growing the carbon nano-tube may utilize theabove-described metal growing process to form catalytic metal on thesurface of the bottoms of the holes. In this case, the catalytic metalis used to crack a hydrocarbon gas. Otherwise, the emitters may beformed by performing an electrodephoresis process on a pre-synthesizedcarbon nano-structure.

Although, in this embodiment, only one emitter 218 is formed in each ofthe holes of the gate insulating layer 206, more than one emitter 218may be formed in each of the holes. Further, the emitters 218 may becomposed by using semiconductor material such as GaN, TiO₂ and CdS.

Finally, as shown in FIG. 2F, a top electrode layer 220 is formed on thestructure shown in FIG. 2E. The top electrode layer 220 is used as ananode of the electric field emission device and also hermetically sealsthe triode structure fabricated as shown in FIG. 2E.

The top electrode layer 220 may be formed by depositing metal in avacuum by employing one of electron beam deposition, thermal deposition,sputtering, LPCVD (low pressure chemical vapor deposition), sol-gelcomposition, electroplating and electroless plating techniques. Themetal used in forming the top electrode layer 220 may be, e.g., Ti, Nb,Mo or Ta, which is generally used as a getter. Otherwise, the topelectrode layer 220 may contain one of Al, Ba, V, Zr, Cr, W, conductivepolymer material, metallic oxide, metallic nitride and metallic sulfide.Further, the thickness of the top electrode layer 220 preferably rangesabout from 300 nm to 1 μm.

In the meantime, FIGS. 3A to 3F describe cross-sectional views of anelectric field emission device having a triode structure fabricated byusing an anodic oxidation process in accordance with a second preferredembodiment of the present invention.

The second embodiment of the present invention has the sameconfiguration as the first embodiment of the present invention, which isshown in FIGS. 2A to 2F, except that there is formed an anode insulatinglayer 211 in stead of the alumina layer 212.

In the following, a process of fabricating the electric field emissiondevice in accordance with the second embodiment of the present inventionwill be described in detail.

First, as shown in FIG. 3A, a bottom electrode layer 202, a resistivelayer 204 and a gate insulating layer 206 are formed on a supportingsubstrate 200. Although the resistive layer 904 has been described to beformed between the gate insulating layer 206 and the bottom electrodelayer 202, the formation of the resistive layer 204 may be omitted.Then, on the gate insulating layer 206, a gate electrode layer 208, ananode insulating layer 211 and an aluminum layer 210 are sequentiallyformed.

Herein, processes of forming the above-mentioned layers and materialcontained therein are the same as those described with reference to FIG.2A except those for the anode insulating layer 211. The anode insulatinglayer 211 is formed by performing one of electron beam deposition,thermal deposition, sputtering, LPCVD (low pressure chemical vapordeposition), sol-gel composition, electroplating and electroless platingtechniques. The anode insulating layer 211 may contain SiO₂ or metallicoxide and is preferably about 500 nm in thickness. Further, in etchingthe anode insulating layer 211, there may be employed one of ionmilling, dry etching, wet etching and anodic oxidation techniques.

Next, as shown in FIG. 3B, the aluminum layer 210 is processed by usingan anodic oxidation process to become an alumina layer 212 havingsub-micro holes 213 therein.

Subsequently, as shown in FIG. 3C, a barrier layer 214 of the aluminalayer 212, the anode insulating layer 211 and the gate electrode layer208 is dry-etched. Then, as illustrated in FIG. 3D, the gate insulatinglayer 206 is etched to have sub-micro holes therein connecting to thecorresponding holes of the alumina layer 212.

Thereafter, as shown in FIG. 3E, the alumina layer 212 is removed andthen emitters 218 are formed in the holes of the gate insulating layer206. The process of removing the alumina layer 212 may be carried out bydipping the alumina layer 212 in a solution of phosphoric acid or amixed solution of phosphoric acid and chromic acid.

Finally, as shown in FIG. 3F, a top electrode layer 220 is formed on thestructure as shown in FIG. 3E. The top electrode layer 220 is used as ananode of the electric field emission device and also hermetically sealsthe triode structure fabricated as shown in FIG. 3E.

Even though the detailed descriptions on material contained in thelayers, the processes of fabricating the layers and the dimensions ofthe layers are not given in the above with reference to FIGS. 3A to 3F,throughout the several views in the accompanying drawings, likereference numerals designate corresponding parts and thus thedescriptions given with reference to FIGS. 2A to 2F are also applicableto the corresponding parts shown in FIGS. 3A to 3F.

While the invention has been shown and described with respect to thepreferred embodiments, it will be understood by those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. An electric field emission device having a triode structurefabricated by using an anodic oxidation process, comprising: asupporting substrate; a bottom electrode layer formed on the supportingsubstrate, which is used as an cathode electrode of the device; a gateinsulating layer formed on the bottom electrode layer, the gateinsulating layer having a plurality of first sub-micro holes to be usedas gate holes of the device; a gate electrode layer formed on the gateinsulating layer, the gate electrode layer having a plurality of secondsub-micro holes each connecting to a corresponding one of the firstsub-micro holes; an alumina layer formed on the gate electrode layer,the alumina layer having a plurality of third sub-micro holes eachconnecting to a corresponding one of the second sub-micro holes; a topelectrode layer for hermetically sealing the device in a vacuum, whichis formed on the alumina layer and used as an anode of the device; and aplurality of emitters for emitting electrons in a high electric field,each of the emitters being formed in a corresponding one of the firstsub-micro holes.
 2. The device of claim 1, wherein the emitter containsmetal, semiconductor or carbon material.
 3. The device of claim 2,wherein the carbon material is selected from a group consisting a carbonnano-fiber, a carbon nano-tube, a carbon nano-particle and amorphouscarbon material.
 4. The device of claim 1, further comprising aresistive layer formed between the bottom electrode layer and the gateinsulating layer;
 5. The device of claim 4, wherein the resistive layercontains SiO₂ or metallic oxide.
 6. An electric field emission devicehaving a triode structure fabricated by using an anodic oxidationprocess, comprising: a supporting substrate; a bottom electrode layerformed on the supporting substrate, which is used as an cathodeelectrode of the device; a gate insulating layer formed on the bottomelectrode layer, having a plurality of first sub-micro holes to be usedas gate holes of the device; a gate electrode layer formed on the gateinsulating layer, the gate electrode layer having a plurality of secondsub-micro holes each connecting to a corresponding one of the firstsub-micro holes; an anode insulating layer formed on the gate electrodelayer, having a plurality of third sub-micro holes each connecting to acorresponding one of the second sub-micro holes; a top electrode layerfor hermetically sealing the device in a vacuum, which is formed on theanode insulating layer and used as an anode of the device; and aplurality of emitters for emitting electrons in a high electric field,each of the emitters being formed in a corresponding one of the firstsub-micro holes.
 7. The device of claim 6, wherein the emitter containsmetal, semiconductor or carbon material.
 8. The device of claim 7,wherein the carbon material is selected from a group consisting a carbonnano-fiber, a carbon nano-tube, a carbon nano-particle and amorphouscarbon material.
 9. The device of claim 6, further comprising aresistive layer formed between the bottom electrode layer and the gateinsulating layer;
 10. The device of claim 9, wherein the resistive layercontains SiO₂ or metallic oxide.
 11. A method for fabricating anelectric field emission device having a triode structure by using ananodic oxidation process, comprising the steps of: (a) forming a bottomelectrode layer on a supporting substrate, the bottom electrode layerbeing used as an cathode electrode of the device; (b) formingsequentially a gate insulating layer, a gate electrode layer and analuminum layer on the bottom electrode layer; (c) forming a plurality offirst sub-micro holes in an alumina layer by performing an anodicoxidation process on the aluminum layer, thereby transforming thealuminum layer into the alumina layer; (d) etching a barrier layer ofthe alumina layer and the gate electrode layer, thereby a surface of thegate insulating layer being exposed through the first sub-micro holes;(e) forming a plurality of second sub-micro holes in the gate insulatinglayer, thereby each of the first sub-micro holes connecting to acorresponding one of the second sub-micro holes; (f) forming an emitterfor emitting electron in a high electric field in each of the secondsub-micro holes; and (g) forming a top electrode layer for hermeticallysealing the device on the alumina layer in a vacuum, the top electrodelayer being used as an anode of the device.
 12. The method of claim 11,wherein, in the step (c), the anodic oxidation process is performed byusing an electrolyte selected from a group consisting of oxalic acid,sulfuric acid, phosphoric acid and chromic acid.
 13. The method of claim11, wherein, in the step (d), the barrier layer of the alumina layer andthe gate electrode layer are etched by using one of ion milling, dryetching and wet etching techniques.
 14. The method of claim 11, wherein,in the step (e), the gate insulating layer is etched by using one of ionmilling, dry etching, wet etching and anodic oxidation techniques. 15.The method of claim 11, wherein, in the step (f), each of the emittersis formed by growing metal from a bottom of each of the second sub-microholes.
 16. The method of claim 15, wherein the metal is grown byapplying DC or AC voltage (or current) or voltage (or current) pulse toa solution of metal sulfate, metal nitrate or metal chloride.
 17. Themethod of claim 15, wherein the metal is grown by using a solution ofmetal sulfate, metal nitrate or metal chloride after chemicallyactivating a surface of the bottom.
 18. The method of claim 11, wherein,in the step (f), each of the emitters is formed by attaching metal to abottom of each of the second sub-micro holes.
 19. The method of claim11, wherein, in the step (f), each of the emitters is formed by forminga carbon nano-structure on a bottom of each of the second sub-microholes.
 20. The method of claim 19, wherein the carbon nano-structure isone of carbon nano-tube, carbon nano-fiber, amorphous carbon and carbonnano-particle, which are composed by using a thermal decomposition. 21.The method of claim 20, wherein the thermal decomposition is performedby thermally decomposing a gas mixture of hydrocarbon, carbon monoxideand hydrogen at 200-800° C.
 22. The method of claim 19, wherein thecarbon nano-structure is one of carbon nano-tube, carbon nano-fiber,amorphous carbon and carbon nano-particle, which are composed by using aplazma decomposition.
 23. The method of claim 11, wherein, in the step(f), each of the emitters is formed by thiolizing a pre-synthesizedcarbon nano-tube and applying thereto an Au—S chemical compositionprocess.
 24. The method of claim 11, wherein, in the step (f), each ofthe emitters is formed by performing an electrodephoresis process on apre-synthesized carbon nano-structure.
 25. The method of claim 11,wherein, in the step (f), more than one emitter is formed in each of thesecond sub-micro holes.
 26. A method for fabricating an electric fieldemission device having a triode structure by using an anodic oxidationprocess, comprising the steps of: (a) forming a bottom electrode layeron a supporting substrate, the bottom electrode layer being used as ancathode electrode of the device; (b) forming sequentially a gateinsulating layer, a gate electrode layer, an anode insulating layer andan aluminum layer on the bottom electrode layer; (c) forming a pluralityof first sub-micro holes in an alumina layer by performing an anodicoxidation process on the aluminum layer, thereby transforming thealuminum layer into the alumina layer; (d) etching an barrier layer ofthe alumina layer, the anode insulating layer and the gate electrodelayer, thereby a surface of the gate insulating layer being exposedthrough the first sub-micro holes; (e) forming a plurality of secondsub-micro holes in the gate insulating layer, thereby each of the firstsub-micro holes connecting to a corresponding one of the secondsub-micro holes; (f) removing the alumina layer; (g) forming an emitterfor emitting electron in a high electric field in each of the secondsub-micro holes; and (h) forming a top electrode layer for hermeticallysealing the device on the anode insulating layer in a vacuum, the topelectrode layer being used as an anode of the device.
 27. The method ofclaim 26, wherein, in the step (c), the anodic oxidation process isperformed by using an electrolyte selected from a group consisting ofoxalic acid, sulfuric acid, phosphoric acid and chromic acid.
 28. Themethod of claim 26, wherein, in the step (f), the alumina layer isremoved by dipping the alumina layer in a solution of phosphoric acid ora mixed solution of phosphoric acid and chromic acid.
 29. The method ofclaim 26, wherein, in the step (g), each of the emitters is formed bygrowing metal from a bottom of each of the second sub-micro holes. 30.The method of claim 29, wherein the metal is grown by applying DC or ACvoltage (or current) or voltage (or current) pulse to a solution ofmetal sulfate, metal nitrate or metal chloride.
 31. The method of claim29, wherein the metal is grown by using a solution of metal sulfate,metal nitrate or metal chloride after chemically activating a surface ofthe bottom.
 32. The method of claim 26, wherein, in the step (g), eachof the emitters is formed by attaching metal to a bottom of each of thesecond sub-micro holes.
 33. The method of claim 26, wherein, in the step(g), each of the emitters is formed by forming a carbon nano-structureon a bottom of each of the second sub-micro holes.
 34. The method ofclaim 33, wherein the carbon nano-structure is one of carbon nano-tube,carbon nano-fiber, amorphous carbon and carbon nano-particle, which arecomposed by using a thermal decomposition.
 35. The method of claim 34,wherein the thermal decomposition is performed by thermally decomposinga gas mixture of hydrocarbon, carbon monoxide and hydrogen at 200-800°C.
 36. The method of claim 33, wherein the carbon nano-structure is oneof carbon nano-tube, carbon nano-fiber, amorphous carbon and carbonnano-particle, which are composed by using a plazma decomposition. 37.The method of claim 26, wherein, in the step (g), each of the emittersis formed by thiolizing a pre-synthesized carbon nano-tube and applyingthereto an Au—S chemical composition process.
 38. The method of claim26, wherein, in the step (g), each of the emitters is formed byperforming an electrodephoresis process on a pre-synthesized carbonnano-structure.
 39. The method of claim 26, wherein, in the step (g),more than one emitter is formed in each of the second sub-micro holes.